The present invention relates to a liquid crystal display device and liquid crystal display method, and more specifically to a color liquid crystal display device and color liquid crystal display method using a liquid crystal having spontaneous polarization.
The liquid crystal display devices are mainly classified into the reflection type and the transmission type. In the reflection type liquid crystal display devices, light rays incident on the front face of a liquid crystal panel are reflected by the rear face of the liquid crystal panel so that an image is visualized by the reflected light. In the transmission type liquid crystal display devices, an image is visualized by transmitted light from a light source (back-light) provided on the rear face of the liquid crystal panel. Although the reflection type liquid crystal display devices have poor visibility resulting from the reflected light amount varying depending on environmental conditions, they have been widely used as monochrome (such as black and white) display devices for portable calculators, watches, etc. because of their low costs. However, they are not suitable as display devices of personal computers displaying a multi-color or full-color image. For this reason, in general, transmission type liquid crystal display devices are used as display devices of personal computers displaying a multi-color or full-color image.
In addition, currently-used color liquid crystal display devices are generally classified into the STN (Super Twisted Nematic) type and the TFT-TN (Thin Film Transistor-Twisted Nematic) type based on the liquid crystal materials to be used. The STN type liquid crystal display devices have comparatively low production costs, but they are not suitable for the display of a moving image because they are susceptible to crosstalk and comparatively slow in the response rate. In contrast, the TFT-TN type liquid crystal display devices have better display quality than the STN type, but they require a back-light with high intensity because the transmissivity of the liquid crystal panel is only 4% or so at present. For this reason, in the TFT-TN type liquid crystal display devices, a lot of power is consumed by the back-light, and there would be a problem when used with a battery power source. Moreover, the TFT-TN type liquid crystal display devices have other problems including a low response rate, particularly in displaying half tones, a narrow viewing angle, and a difficult color balance adjustment.
Under such circumstances, in the case where a liquid crystal display device is used as a multi-media display device, it is required to have a moving image display characteristic capable of displaying a full moving image. With the currently-used liquid crystal display devices, however, even if images are displayed at a high rate, the liquid crystal display device reaches its limit in displaying around 40 images per second. If full moving images are displayed at a higher rate, for example, at a rate of 60 images per second, the liquid crystal molecules can not act sufficiently, resulting in blurred images.
In order to solve such a problem, it has been known to use a liquid crystal material having spontaneous polarization capable of responding at a rate of several tens to several hundreds μ seconds, for example, ferroelectric liquid crystal material or antiferroelectric liquid crystal material. In a liquid crystal display device using a liquid crystal material having such spontaneous polarization, a passive type panel (simple matrix panel) is usually used. However, in this simple matrix type, since writing of each line is carried out until the liquid crystal molecules have come to a completely still state, it takes 16.6 milliseconds ( 1/60 second) or more to display one image and consequently a full moving image display can not be achieved. Therefore, an active matrix panel, namely a TFT panel is used. With the use of the TFT panel, even when a drive voltage application time per line is shorter than the response time of liquid crystal molecules, the liquid crystal molecules act due to charges introduced into the TFT. Besides, if the liquid crystal molecules show a sufficient response before the next application of a drive voltage, a full moving image display can be achieved without problems. Furthermore, with the use of the TFT panel, it is possible to readily control half-tone display.
As described above, with a color liquid crystal display device constructed by sealing a coloring material, such as a color filter, and ferroelectric liquid crystal material or antiferroelectric liquid crystal material in a TFT panel, it is possible to achieve a full moving image display compatible with multimedia. However, in the event where this full moving image display is observed in detail, when a displayed image is moved, the outline portion of the image along a direction perpendicular to the moving direction is seen as a blur. Moreover, as the moving speed increases, the blur of the outline portion becomes more noticeable, resulting in degradation of the image quality. Such a phenomenon can be explained by the following theory.
FIG. 1 is a schematic diagram showing a basic image which is used for the purpose of explaining the theory. As shown in FIG. 1, this basic image is a white square image with a black background. In the case where the basic image as shown in FIG. 1 is displayed as a still image, since the image is fixed, the square image can be observed clearly.
Next, display of a moving image will be considered. Here, for a display of this white square image as a moving image, suppose that this image moves in the right direction at a constant rate (for example, three pixels/frame). FIG. 2 is an illustration showing the pixel position in each frame during the display of moving image. In FIG. 2, the vertical axis is a time axis, while the horizontal axis indicates pixels on a certain line on a liquid crystal panel. Here, the moving image is displayed on the liquid crystal panel in such a manner that the image having a black background and a white portion in the width of four pixels moves by an amount of three pixels per frame in a direction in which the pixel number increases. Thus, as shown in FIG. 2, in the n frame, R, G, B display data are displayed from the m pixel to the m+3 pixel, and in the n+1 frame, similarly, R, G, B display data are displayed from the m+3 pixel to the m+6 pixel.
When observing such a moving image, the observer views the image while moving his/her eyes as the image moves. Therefore, as shown by arrow A in FIG. 2, the point at which the observer's eyes are turned moves by an amount of three pixels per frame in the image moving direction. The reason why the observer moves his/her eyes in such a manner when observing the moving image is to cause the moving image to always stay in the same position on the retina of the observer. Consequently, the observer recognizes an image as shown in FIG. 3.
FIG. 3 is an illustration showing an image state when a moving image display is viewed. In FIG. 3, similarly to FIG. 2, the vertical axis is the time axis, while the horizontal axis indicates the pixels on a certain line on the liquid crystal panel. Moreover, an image that is actually recognized by the observer (the observation result) is shown on the lower side of FIG. 3, which indicates that the higher the pitch of the slanting lines, the darker the image recognized. Furthermore, arrow A corresponds to the arrow A shown in FIG. 2, and indicates the movement of the point at which the observer's eyes are turned. In the case where a moving image is displayed, the eyes follow the target moving image. For instance, when the moving image is viewed by focusing the observer's eyes on the outline portion shown by the arrow A, since the target moving image is seen as if it is a still image on the retina, the displayed image of FIG. 2 is seen as if it is the observation result shown in FIG. 3 on the retina.
Since the point at which the observer's eyes are turned moves with a movement of the image, the displayed R, G, B display data are observed as if they are flowing in the direction opposite to the moving direction of that point (the direction in which the pixel number decreases). In other words, the R. G, B display data are observed as if they are drugged in the direction in which the pixel number decreases. In the case where the moving image is observed in such a manner, since the R, G, B display data are separated from each other in a time direction, degradation of the image quality of the outline portion is observed as shown in FIG. 3. More specifically, although the white image is displayed, the outline portion of the image is observed as a dark blur.
As described above, the outline portion of the image which is clearly displayed as a still image is seen as a blur as shown in FIG. 3 by following the moving image, and the outline portion is observed over several pixels. Hence, when this display device is used as a multimedia display device for displaying moving images, it causes a problem that degradation of the image quality occurs in displaying moving images.
FIGS. 2 and 3 schematically illustrate the state, and, in actual, since the pixel pitch is small, the outline portion of a moving image is not seen as a blur at a rate of around 3 dots per frame. However, when an image moves at an extremely high rate and the human's eyes can follow the moving image, degradation of the image quality as shown in FIG. 3 will be observed.